Looks good to me. Too small of a tank and its to the point of being mean to the horses (unless going dwarfs), too big of a tank and it gets difficult to ensure they're getting fed. Filtration wise, I've heard/read both sides as to whether a protein skimmer is needed or not. Personally, I use one with my horses (and they enjoy using the plastic air pipes to hitch on), it's a backpack style, along with a standard material/carbon filter. Need to make sure though that they have plenty of area in the tank that is calm, without heavy water flow from filtration. They have a hard time eating/perching otherwise. That said, they DO enjoy playing in the heavier flow areas at time, fun to watch. Also make sure you don't go too heavy on the heater with the horses, above ~75 and it's asking for parasite trouble with them.